The present invention relates to an antenna device and a portable equipment, and more particularly, relates to an antenna device capable of preventing degradation in antenna gain during a call, and a portable equipment using the same.
Recently, mobile phones are increasingly becoming widespread. FIG. 17 is a schematic diagram of a conventional mobile phone, and FIG. 18 shows a schematic cross-sectional view taken along line XVIIIxe2x80x94XVIII of FIG. 17 and a schematic graph of a current distribution in an antenna. The conventional mobile phone will now be described with reference to FIGS. 17 and 18.
Referring to FIGS. 17 and 18, a conventional mobile phone 101 includes in its main body a liquid crystal display portion 105, operation keys 106 for inputting a telephone number and the like, a speaker 104 and a microphone 103 for listening and speaking over the phone, respectively, and an antenna for communication with a base station. The antenna, which is formed from a non-retracted antenna 151 and a linear extension antenna 102, is retractable in the main body of mobile phone 101. FIGS. 17 and 18 show the state where the antenna is retracted in the main body of mobile phone 101. As shown in FIGS. 17 and 18, when the antenna is retracted in main body 108 of mobile phone 101, non-retracted antenna 151 sticks out of main body 108, and extension antenna 102 is accommodated within main body 108. On the other hand, when mobile phone 101 is used for a phone call or the like, the antenna is stretched out of main body 108 of mobile phone 101 as shown in FIG. 19 so that extension antenna 102 is exposed outside main body 108. FIG. 19 shows a schematic cross sectional view of the state where the antenna is stretched out of the main body of the mobile phone of FIG. 17 and a schematic graph of a current distribution in the antenna. FIG. 19 corresponds to FIG. 18.
Referring to FIGS. 18 and 19, the mobile phone includes a metal boss 150 in order to fix the antenna formed from non-retracted antenna 151 and linear extension antenna 102 to main body 108 in a stretchable manner. Metal boss 150 is a cylindrical boss having a hole, and the antenna is slidably inserted into the hole. When the antenna is retracted as shown in FIG. 18, the antenna is fixed by contact between the sidewall of the hole in metal boss 150 and the surface of the region of the antenna that is located under non-retracted antenna 151. When the antenna is stretched as shown in FIG. 19, the antenna is fixed by contact between the sidewall of the hole in metal boss 150 and the surface of an antenna end 111 located at the end of the antenna.
Metal boss 150 is fixed to a housing of main body 108 of mobile phone 101, and the like. Main body 105 of mobile phone 101 accommodates therein a circuit substrate 109 having transmitting/receiving circuit elements arranged thereon. A power feed pin 110 is mounted on the surface of circuit substrate 109. Power feed pin 110 contacts the outer peripheral surface of metal boss 150.
When the antenna is retracted as shown in FIGS. 17 and 18, the circuit elements formed on circuit substrate 109 are electrically connected to non-retracted antenna 151 through power feed pin 110, metal boss 150 and the region of the antenna that is located under non-retracted antenna 151. Moreover, when the antenna is stretched as shown in FIG. 19, the circuit elements formed on circuit substrate 109 are electrically connected to extension antenna 102 through power feed pin 110, metal boss 150 and antenna end 111.
However, the conventional mobile phone of FIGS. 17 to 19 has the following problems.
Since metal boss 150 contacting the antenna is also a conductor, it acts as if it were a part of antenna when the antenna transmits and receives radio waves. For example, when a current flows through non-retracted antenna 151 of FIG. 18 (e.g., when non-retracted antenna 151 receives radio waves), it flows not only through non-retracted antenna 151 but also through metal boss 150. Moreover, when extension antenna 102 of FIG. 19 transmits and receives radio waves, a current flows not only through extension antenna 102 but also through metal boss 150. In other words, due to the presence of metal boss 150, non-retracted antenna 151 and extension antenna 102 act as if they were an antenna having an electrically discontinuous diameter. Accordingly, the current distribution in the antenna does not have a sinusoidal profile, as shown in FIGS. 18 and 19. With such a non-sinusoidal current distribution in the antenna, target impedance characteristics cannot be obtained even if the respective lengths of non-retracted antenna 151 and extension antenna 102 are designed so that they resonate in response to the radio waves of a target frequency.
Moreover, as shown in FIGS. 18 and 19, the presence of metal boss 150 increases a current value in the region near main body 108 of mobile phone 101. This results in increased electric-field and magnetic-field strengths (electromagnetic-field strength) in the region near main body 108. The user holds main body 108 of mobile phone 101 by hand and also holds main body 108 near the head for a phone call. In this case, since metal boss 150 of main body 108 located in a region relatively close to the human body produces a relatively strong electromagnetic field, the presence of the human body affects the antenna gain more strongly. The antenna gain is thus reduced by the influence of the human body, resulting in degraded communication quality.
Moreover, metal boss 150 is formed from a metal having relatively larger specific gravity than a material of the housing of mobile phone 101 and the like such as plastic. Reduction in size and weight has been strongly demanded for mobile phone 101, and the use of a metal boss is one of the factors that hinder reduction in weight of the mobile phone.
The present invention is made to solve the above problems, and it is an object of the present invention to provide an antenna device and a portable equipment that are capable of preventing degradation in communication quality.
It is another object of the present invention to provide an antenna device and a portable equipment that enable reduction in weight.
An antenna device according to one aspect of the present invention includes a linear antenna, a fixing member and a power feed member. The fixing member is formed from a dielectric, and holds a portion of the antenna. The power feed member contacts the antenna. The fixing member holds the antenna in a movable manner.
In this structure, the fixing member such as a boss for holding a portion of the antenna is formed from a dielectric, whereby the antenna and the fixing member can be prevented from acting as if they were an antenna having an electrically discontinuous diameter. As a result, a current flowing through the antenna can be prevented from unnecessarily flowing through the fixing member. This enables the current distribution in the antenna to have an approximately sinusoidal profile, whereby the impedance characteristics of the antenna can be prevented from being varied from the designed characteristics.
When the antenna device of the present invention is applied to a portable equipment such as a mobile phone, the fixing member is mounted to the main body of the portable equipment. In using such a portable equipment, the main body thereof is often held by hand and retained near the head of the human body. In other words, the fixing member is located in a region relatively close to the human body. In the antenna device of the present invention, the fixing member is formed from a dielectric, so that no current will unnecessarily flow through the fixing member. Accordingly, an electromagnetic field that is conventionally formed by the current flowing through the fixing member will not be formed. Since a current flowing through the antenna thus produces a weaker electromagnetic field in the region relatively close to the human body as compared to the conventional example, characteristics such as antenna gain can be less affected by the presence of the human body. As a result, the characteristics such as antenna gain can be prevented from being degraded by the influence of the human body.
Moreover, since the fixing member is formed from a dielectric, a material such as a resin having relatively smaller specific gravity than a metal used in the conventional example can be used as a material of the fixing member. As a result, by applying the antenna device of the present invention to a portable radio equipment such as a mobile phone, the weight of the portable radio equipment can be reduced as compared to the case of using a metal fixing member.
In the antenna device according to the aforementioned one aspect, the fixing member may have an opening for exposing a part of a surface of the portion of the antenna that is held by the fixing member, and the power feed member may contact the part of the surface of the antenna through the opening.
In this case, electrical connection between the power feed member and the antenna can be implemented with the fixing member having a relatively simple structure, i.e., the fixing member having an opening. As a result, the structure of the antenna device can be simplified. Moreover, complicated processing is not required such as embedding the power feed member into the wall of the fixing member, enabling reduction in manufacturing costs of the antenna device.
In the antenna device according to the aforementioned one aspect, the antenna may include an extended portion extending out of the fixing member, and the power feed member may be mounted in contact with the extended portion.
In this case, since the contact between the antenna and the power feed member is ensured in a region other than the region where the fixing member is located, connection between the antenna and the power feed member can be assured without requiring special processing such as providing the fixing member with a conductive wire that contacts the antenna. This enables a further simplified structure of the antenna device and reduction in manufacturing costs thereof.
In the antenna device of the aforementioned one aspect, the fixing member is preferably a cylindrical member having a hole, and the antenna is preferably inserted in the hole of the cylindrical fixing member.
In this case, when a region of the antenna that is fixed to the fixing member has an outer diameter that is approximately the same as the hole diameter of the fixing member, the position of the antenna relative to the fixing member can be easily determined by making that region in contact with the sidewall of the hole in the fixing member.
In the antenna device according to the aforementioned one aspect, the power feed member may contact the antenna within the hole of the fixing member.
In this case, since the power feed member and the antenna contact each other within the fixing member, the volume of the region occupied by the antenna device can be reduced as compared to the case where the power feed member and the antenna contact each other outside the fixing member. As a result, reduction in size of the antenna device can be achieved.
In the antenna device according to the aforementioned one aspect, the fixing member is preferably formed from a resin.
In this case, the fixing member can be easily formed due to better processability of the resin than that of a metal or the like.
A portable equipment according to another aspect of the present invention includes a housing, a linear antenna, a fixing member and a power feed member. The fixing member is formed from a dielectric, and holds a portion of the antenna so as to fix the antenna to the housing. The fixing member holds the antenna in a movable manner. The power feed member contacts the antenna.
In this structure, the fixing member such as a boss for holding a portion of the antenna is formed from a dielectric, whereby the antenna and the fixing member can be prevented from acting as if they were an antenna having an electrically discontinuous diameter. As a result, a current flowing through the antenna can be prevented from unnecessarily flowing through the fixing member. This enables the current distribution in the antenna to have an approximately sinusoidal profile, whereby the impedance characteristics of the antenna can be prevented from being varied from the designed characteristics. As a result, degradation in communication quality can be prevented in the portable equipment such as a mobile phone and a radio device.
Since the antenna is mounted to the portable equipment, the fixing member is mounted to the main body of the portable equipment. In using such a portable equipment, the main body thereof is often held by hand and retained near the head of the human body. In other words, the fixing member is located in a region relatively close to the human body. In the portable equipment of the present invention, the fixing member is formed from a dielectric, so that no current will unnecessarily flow through the fixing member. Accordingly, an electromagnetic field that is conventionally formed by the current flowing through the fixing member will not be formed. Since a current flowing through the antenna thus produces a weaker electromagnetic field in the region relatively close to the human body as compared to the conventional example, characteristics such as antenna gain can be less affected by the presence of the human body. As a result, the characteristics such as antenna gain can be prevented from being degraded by the influence of the human body.
Moreover, since the fixing member is formed from a dielectric, a material such as a resin having relatively smaller specific gravity than a metal used in the conventional example can be used as a material of the fixing member. As a result, the weight of the portable equipment can be reduced as compared to the case of using a metal fixing member.
In the portable equipment according to the aforementioned another aspect, the fixing member may have an opening for exposing a part of a surface of the portion of the antenna that is held by the fixing member, and the power feed member may contact the part of the surface of the antenna through the opening.
In this case, electrical connection between the power feed member and the antenna can be implemented with the fixing member having a relatively simple structure, i.e., the fixing member having an opening. As a result, the structure of the portable equipment can be simplified. Moreover, complicated processing is not required such as embedding the power feed member into the wall of the fixing member, enabling reduction in manufacturing costs of the portable equipment.
In the portable equipment according to the aforementioned another aspect, the antenna may include an extended portion extending out of the fixing member within the housing, and the power feed member may be mounted in contact with the extended portion.
In this case, since the contact between the antenna and the power feed member is ensured in a region other than the region where the fixing member is located, connection between the antenna and the power feed member can be assured without requiring special processing for the fixing member such as providing the fixing member with a conductive wire that contacts the antenna. This enables a further simplified structure of the portable equipment and reduction in manufacturing costs thereof.
In the portable equipment according to the aforementioned another aspect, the fixing member is preferably a cylindrical member having a hole, and the antenna is preferably inserted in the hole of the cylindrical fixing member.
In this case, when a region of the antenna that is fixed to the fixing member has an outer diameter that is approximately the same as the hole diameter of the fixing member, the position of the antenna relative to the fixing member can be easily determined by making that region in contact with the sidewall of the hole in the fixing member.
In the portable equipment according to the aforementioned another aspect, the power feed member may contact the antenna within the hole of the fixing member.
In this case, since the power feed member and the antenna contact each other within the fixing member, the volume of the region required for the connection between the power feed member and the antenna can be reduced as compared to the case where the power feed member and the antenna contact each other outside the fixing member. As a result, reduction in size of the portable equipment can be achieved.
The portable equipment according to the aforementioned another aspect may further include a substrate held within the housing. The power feed member may include a conductor member contacting the portion of the antenna that is held by the fixing member, and being connected to the fixing member, and an electrode contacting the conductor member and mounted on the substrate.
In this case, the antenna can be electrically connected to circuit elements on the substrate through the conductor member and the electrode. Since the electrode need only have a contact surface that contacts the conductor member, a simply structured conductor member on the substrate such as a conductor film or electrode plate mounted on the substrate can be used as the electrode. As a result, the structure of the substrate can be simplified as compared to the case where a structure such as a power feed pin is mounted on the substrate.
In the portable equipment according to the aforementioned another aspect, the fixing member is preferably formed from a resin.
In this case, the fixing member can be easily formed due to better processability of the resin than that of a metal or the like.